Fuel cells have attracted considerable interest in the past two decades, mainly because of the increasing need to improve energy efficiency, as well as to address concerns on the environmental consequences of using fossil fuel for electricity generation and vehicle propulsion. Small fuel cell systems producing about 1 to about 100 kW power output are desirable for light-duty vehicles and auxiliary power supply units (APU) and have been recognized among the most successful applications of fuel cell technology so far.
However, the lack of an appropriate infrastructure for producing and distributing H2 fuel is substantially hindering further developmental and commercialization activities of fuel cell technology. This has intensified research activities on fuel reforming, through which a fossil fuel is catalytically broken down to form a gas mixture of H2, CO2, H2O and CO. The fuel cell systems can then operate efficiently with the conventional liquid hydrocarbon fuels, such as ethanol, gasoline and diesel, and thus hydrogen storage and transportation problems could be avoided.
Among suitable liquid fuels that can be reformed, diesel is of particular interest, owing to its high energy density, well-established distribution infrastructure, relatively low price and ease of handling. In general, the conversion of diesel fuel to hydrogen-rich gas products can be carried out by three main reaction processes, namely steam reforming (SR), partial oxidation (POX) and autothermal reforming (ATR). Designating diesel fuel as CnHm, these three different catalytic reforming approaches can be described as follows:SR: CnHm+H2O→COx+H2 ΔHf>0POX: CnHm+O2→CO2+H2(+H2O) ΔHf<0ATR: CnHm+H2O+O2→COx+H2 ΔHf˜0                where n=˜10 to 20 and x=1 or 2.        
ATR, being considered as a combination of the endothermic SR reaction and the highly exothermic POX reaction, allows the control of the total heat balance by adjusting the feed proportions of diesel fuel, air and steam, and is much less externally energy-intensive and thus cost-effective. In addition, the ATR process offers simpler reactor design, lower operation temperature and more dynamic response to work under varying load. It is also postulated that the water-gas-shift (WGS) reaction shown below plays a significant role in the diesel AIR process, which may help further increase the hydrogen yield in the final ATR products:WGS: CO+H2OCO2+H2 
Nevertheless, the diesel ATR is still a great challenge nowadays, especially on the ATR catalyst development. For example, the presence of heavy polyaromatics in the diesel poses a threat of carbon formation (i.e. coking) on the catalytically active sites and thus deactivates the catalyst itself. This is particularly the case for most Ni-based catalysts and even some noble-metal catalysts. Moreover, the kinetics of polyaromatics reforming reaction is much slower than that of other components in the diesel fuel such as paraffins, which usually requires higher operation temperature and may in turn cause excessive sintering of metal catalysts.
Another major challenge is from the inherently existing sulfur species, which can readily react with transition metals and form stable metal sulfide, resulting in the deactivation of the catalyst systems. Some noble-metals (e.g. Ru, Rh, Pt) were reported to pose excellent catalytic activity towards diesel reforming, while critical issues like sulfur poisoning and long-term operation stability have yet been addressed. 1% Pt/ceria catalyst has been shown to exhibit good stability for the ATR of synthetic diesel fuel (sulfur-free) but was severely poisoned in the sulfur containing fuel. It was also reported that, up to 10% Ni in the Rh—Ni/CeO2—Al2O3 catalyst system could act as a protective and sacrificial metal for Rh, and contribute to a much higher sulfur tolerance, i.e. more than 95% conversion in sulfur-containing fuel (22 ppm S) for 72 hrs. Such performance is not satisfactory to drive fuel cell systems. The high cost of noble metals is another great commercial obstacle for their widespread use.
The beneficial effect of oxygen-ion conductivity for the catalytic reforming of hydrocarbons has recently been reported. It was found that, noble metals such as Pt or Rh were more active when supported on ceria compared to when supported on alumina. The inherent oxygen-ion conductivity in ceria may contribute to the water dissociation on the ceria surface and subsequently oxygen transfer to the supported metals, which may result in carbon gasification at elevated temperatures, and then help to maintain a carbon-free catalyst surface.
Perovskite oxides with a typical formula ABO3 have been known and reported for their mixed oxygen-ion and electronic conductivity. However, the use of such perovskite oxides has been mainly focused on solid oxide fuel cell applications or ceramic membrane applications.
Thus, there remains a need to provide for a catalyst system that overcomes, or at least alleviates, the above-mentioned coking and/or sulfur-poisoning problems.